3D printing of porous polymeric materials for stationary phases of chromatography columns
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The work described in this thesis focused on the creation of 3D printed chromatography columns using high internal phase emulsion polymer (polyHIPE) materials. The first step was to prepare and optimize a porous, polymeric stationary phase for chromatography. An approach used throughout the work was based on a special type of emulsion polymerization, the HIPE, which results in a highly porous, interconnected structure, in which the pore size and pore size distribution can be tightly controlled. Glycidyl methacrylate (GMA) is a reactive monomer that is frequently used for the preparation of functional polymers. The possibility of preparation of materials with a high level of porosity (up to 90%), pore size tuning and the availability of an epoxy reactive group for further chemical modification to include adsorptive ligands make GMA-based polyHIPEs good candidates for chromatographic applications.
Photo polymerization of GMA-based HIPE was achieved with a UV lamp operating at a 300-400 nm wavelength. Scanning electron microscopy and the Brunauer–Emmett–Teller method were used to analyze the size and distribution of porosity as well as the surface area of the materials.
The polyHIPE materials reported to date have typically been weak and brittle, with a chalky consistency that crushes and readily breaks down under applied stress. The mechanical properties of the prepared porous polyHIPE materials were therefore improved using crosslinkers or co-crosslinkers of high molecular weights (average MW 286 and 550 g mol-1). The Young’s modulus of GMA-based polyHIPEs containing 40% PEGDMA increased by 50% and the crush strength by 400% when compared with traditional GMA/Ethylene glycol dimethylacrylate polyHIPEs. Subsequent morphological studies showed that the mechanically improved foams possessed the characteristic interconnected pore structure and properties of typical polyHIPEs, meaning that mechanical strength was improved without a loss of the desired high internal porosity.
For the first time, 3D-printed chromatographic columns were created from poly(HIPE) materials, using a digital light processing 3D printer that was developed to polymerize GMA-based HIPEs through control of UV scattering, light penetration and the monomer surface. Chromatographic columns (column size: 100 mL) with complex but uniform internal flow channel geometries (gyroids) with 50% porosity and 500 μm channel diameter were created by computer aided design and printed layer-by-layer using the DLP printer. The GMA backbone epoxy groups in the printed columns were then chemically functionalized with diethylaminoethyl groups to create a printed anion exchange chromatography column. Residual carboxylic groups were capped with ethanolamine to remove cationic charges to ensure only anionic modality in the column.
The chromatographic performance of the functionalized, printed column with and without mechanical improvement was assessed using an ion-exchange chromatography system. The static BSA binding capacity of the basic printed, functionalized had a maximum protein capacity of 160 mg BSA g-1 polyHIPE, while it was 140 mg BSA g-1 polyHIPE for the mechanically improved one. The dynamic binding capacity of the mentioned monoliths was also measured in different flow rates from 0.5 ml min-1 to 6 ml min-1 and the maximum dynamic binding capacity at 50% breakthrough was 13.56 mg ml-1 polyHIPE. A complete separation of cytochrome C from BSA was achieved on both printed monoliths. This was done using an ion-exchange chromatography system, testing and optimizing the printed columns with different bimolecular solutions. Finally, the results show, for the first time, that the printed crosslinked GMA-based polyHIPE material is a promising material a stationary phase for separation of biomolecules in chromatography.